The goal of these studies is to better understand the role of postsynaptic acetylcholine receptors in the synaptic competition that occurs at the vertebrate neuromuscular junction. Synaptic competition, which leads to the loss during postnatal development of some of the synapses established earlier, is a fundamental but poorly understood process occurring throughout the developing nervous system and perhaps also during learning and memory formation. The neuromuscular junction offers unparalleled access into the underlying mechanisms. For example, because this is one of very few synapses that can be observed over time in living animals, it is possible to follow dynamic events such as synaptic competition directly at this synapse in situ. Previous work has suggested postsynaptic receptors are regulated in an important way during synaptic competition. In these studies synaptic competition will be followed in living animals using sophisticated image processing and other techniques that will permit receptor rearrangements to be analyzed. It is hoped that these experiments will help transform the largely theoretical questions of synaptic competition into questions of cell biology.